1. Field of the Invention
The present invention relates to a method and a system for automatic management of the spacing of at least one aircraft, referred to as reference aircraft, behind at least one other aircraft, referred to as target aircraft, preceding it.
2. Discussion of Prior Art
It is desirable, in order to maintain a spacing, to apply speed control commands to the reference aircraft (or following aircraft) such that they allow said reference aircraft to adopt the same position, the same speed, and the same acceleration as the target aircraft (or aircraft being followed) N seconds before the current time (or present time), N seconds corresponding to a predetermined period of time.
The present invention may be applied to a cruising phase, in particular to make a fleet of aircraft, for example cargo planes, fly behind one another. It may also be applied to a descent phase or an approach phase prior to landing, in particular on an airport runway.
With regard to such an approach, it is known that, due to the ever-increasing air traffic, new methods are being sought for avoiding saturation of the busiest airport platforms. One of these methods consists in delegating to an aircraft (following aircraft), in particular a cargo plane, the automatic performance of a spacing maneuver with respect to another aircraft (aircraft being followed) flying in front of it, within the terminal areas of the air traffic control. In order to implement such a method, an air traffic controller indicates to the following aircraft, by means of a usual radio communications system, which aircraft it must follow, the type of maneuver to be carried out, and the value of the spacing with which it must comply. The performance of such an automatic spacing maneuver allows the landing and take-off capacities of the runways of an airport to be increased, by optimizing the distances between the aircraft (during landing and during take-off).
From the document FR-2 925 711 (U.S. Pat. No. 8,108,088), a method and a device are known for automatic guidance, during a landing procedure, of a following aircraft which follows a preceding aircraft, with a particular spacing according to a spacing maneuver. This method and this device allow spurious engine power applications to be avoided, by automatically controlling, during the whole spacing maneuver, the current energetic state of the following aircraft, in order for it to remain compatible with the execution of an approach procedure leading up to a landing (with, if necessary, a limitation in the guidance commands relating to the speed).
Furthermore, from the document FR-2 968 440 (U.S. Publication 2013/0261945), a system is known for automatic management of the spacing of a reference aircraft behind at least one target aircraft, which comprises a device for implementing an acquisition function allowing a given spacing between this reference aircraft and the target aircraft to be automatically acquired at a merge waypoint and a hold function which allows this spacing to be automatically maintained following its acquisition. This device comprises calculation means relating to said acquisition function which determine speed control commands which are applied to the reference aircraft in order for it to perform the acquisition of said spacing at said merge waypoint.
Such a device uses information relating to the distance of the target aircraft with respect to the merge waypoint for determining said speed control commands which are applied to the reference aircraft.
Four types of acquisition maneuvers are notably possible:
a following maneuver (referred to as “Remain Behind”): the two aircraft follow the same route, and the acquisition is to be carried out within a reasonable period of time (time constraint);
a convergence maneuver (referred to as “Merge then Remain Behind”): the two aircraft having a common flightplan after a merge waypoint (or convergence point), the acquisition must be carried out at the latest at this merge waypoint (spatial constraint). The target aircraft is presumed to fly directly toward the merge waypoint;
a heading away and convergence maneuver (referred to as “Vector then Merge Behind”): the reference aircraft (or following aircraft) initially following a given heading, a flight management system calculates a path heading away for this reference aircraft, followed by a convergence to a merge waypoint, where the acquisition is to be carried out at the latest at this merge waypoint. The target aircraft is assumed to fly directly toward the merge waypoint; and
a hold and convergence maneuver (referred to as “Follow route then Merge Behind”): the reference aircraft following its scheduled route, a management system for the flight calculates a path comprising a direct segment toward the merge waypoint starting from a point which is correctly positioned along the flightplan in order to carry out the acquisition at said merge waypoint. The target aircraft is presumed to fly directly toward the merge waypoint
In all of these maneuvers, it is assumed that the target aircraft flies directly toward the merge waypoint.
This assumption of direct flight (in other words following a rectilinear segment between the current position of the target aircraft and the position of the merge waypoint) does not however allow a correct and satisfactory acquisition of the spacing whenever the path of the target aircraft is significantly different from a direct path toward the merge waypoint.
Indeed, in such a situation, the target aircraft will take a significantly longer time to reach the merge waypoint than predicted.
Moreover, for flight paths having particularly complex geometries, the direct distance may even, over time, stop decreasing and locally re-increase. The effect on the guidance of the following aircraft may consist of an unnecessary acceleration at the start of the acquisition, followed by an abrupt deceleration at the end of the acquisition, which can lead to a degradation in comfort and potentially an incapacity to perform a correct acquisition resulting in a cancellation of the maneuver. As such a situation is not rare, it leads to a significant limitation of the possibility of using the usual acquisition function.